Add Travis tests

[sandrokeil]

The driver should be tested for different Linux and PHP versions.

• PHP >= 7.1
• Debian / Ubuntu / Alpine

[sandrokeil]

Currently only Alpine with PHP 7.1 is tested.

[LaravelFreelancerNL]

I'd like to help out, what do you need?

[sandrokeil]

@LaravelFreelancerNL I am happy to hear that. :-) You can start with the following. Please use our new branch for native driver for your PRs.

• PHP 7.1 with Alpine 3.6
• PHP 7.1 with Alpine 3.7
• PHP 7.2 with Alpine 3.6
• PHP 7.2 with Alpine 3.7
• PHP 7.1 with Debian Jessie
• PHP 7.2 with Debian Stretch
• Nightly allow fail

I'm not sure if we can do all of them with Travis natively. The current test uses PHP 7.1 and 7.2.

[LaravelFreelancerNL]

Is this project still active or has it been abandoned?
I'll have time to test soon.

[sandrokeil]

It's still alive, but we are working on different things. So, at the moment there is nothing to do due the refactoring.